Procede d&#39;hydrotraitement et/ou d&#39;hydrocraquage de charges azotees avec stripage a l&#39;hydrogene

ABSTRACT

The invention relates to a process for hydrotreatment and/or hydrocracking of nitrogen feedstocks in which a portion of the hydrotreated and/or hydrocracked effluent is recycled to the hydrotreatment and/or hydrocracking stage after having been subjected to stripping with hydrogen or any other inert gas. 
     The invention is particularly well suited for the processes that are performed in the absence of gaseous hydrogen circulating through the catalytic bed.

The invention relates to a process for hydrotreatment and/or hydrocracking of nitrogen feedstocks.

These types of treatment are extensively described in literature, whether this is with supply of gaseous hydrogen, most often mixed with the feedstock, or whether this is in the absence of circulation of gaseous hydrogen through the catalytic bed, whereby the hydrogen is then entirely dissolved in the treated feedstock on the catalytic bed (for example, in the U.S. Pat. No. 6,428,686).

It was already noted that in the presence of acid catalyst, the gaseous ammonia released by the reaction had a negative effect on the catalytic performances.

Thus, in the patent FR-2,830,870, a hydrotreatment process is described that is followed by a hydrocracking, in the presence of gaseous hydrogen, in which the hydrotreated effluent is subjected, before hydrocracking, to a hot flash for separating the ammonia so as to obtain an effluent that contains less than 1,500 ppm by weight of ammonia (calculated nitrogen), and for a hydrocracking, this quantity is greater than 100 ppm by weight (calculated N).

In the U.S. Pat. No. 6,428,686, a portion of the hydrotreated and/or hydrocracked effluent is recycled directly (without separation) in the feedstock that goes to the hydrotreatment and/or hydrocracking reactor, or else the hydrotreated and/or hydrocracked effluent passes in a flash, and a portion of the separated liquid is recycled to the reactor. The recycled portion as well as the feedstock are brought into contact with gaseous hydrogen in a chamber and then are subjected to a flash so as to separate the gaseous hydrogen before being sent into the reactor. In practice, the flash and the reactor can be in the same chamber, whereby the flash is placed in a disengagement zone upstream from the catalytic bed. It is then said that the reaction is performed in the absence of circulation of gaseous hydrogen through the catalytic bed.

In the known configurations, such as those described above, the effluent is subjected to a flash with a significant pressure drop. As a result, the transfer (such as the recycling) of the effluent requires a large pump, and the more it is desired to reduce the content of ammonia in the effluent, the greater the pressure drop and the pump size will consequently be. This greatly affects the economy of the process, in particular in the processes that are performed in the absence of the circulation of gaseous hydrogen, processes of which the object was specifically to reduce the costs.

The process according to the invention proposes a simple, economic and effective means that maintains, restores, or improves the catalytic performances. In this process, at least 80%, and most often at least 90%, of the ammonia is eliminated from the effluent before recycling. Also, this process makes it possible to keep the effluent from the reactor under conditions that are close to the hydrogen saturation under conditions of pressure and temperature that are close to those of the inlet of the reactor.

To our knowledge, it is virtually impossible to eliminate ammonia from a liquid effluent (i.e., without excess gas) from the reactor by simple flash.

The process according to the invention, due to stripping, also has the advantage of greatly reducing, and even eliminating, other contaminants, in particular H₂S. The light gases are also separated, which increases the weight of the effluent and brings about its saturation by hydrogen more quickly. The result is another advantage relative to the prior art when the stripping is carried out with hydrogen, and in particular within the framework of a process in the absence of circulation of gaseous hydrogen, an advantage that is to reduce the supply of make-up hydrogen at the level of the feedstock to be treated or the reactor.

In these processes that are performed in the absence of circulation of gaseous hydrogen, by using the process according to the invention, it is possible to expect gains in activity, which are generally on the order of 5° C. of hydrodesulfurization (for example, deep hydrodesulfuization of gas oil) or in a more general way in hydrotreatment (such as the hydrotreatment of the fraction of the VGO (vacuum gas oil) or DAO (deasphalted oil) type).

Regarding the hydrocracking, the gains in activity are very high, since they are generally established around 20° C.

In terms of conversion, this means gains of at least 10 points, and even 15 points or more.

More specifically, the process according to the invention is a process for hydrotreatment and/or hydrocracking of nitrogen feedstocks in which a portion of the hydrotreated and/or hydrocracked effluent is recycled to the hydrotreatment and/or hydrocracking stage after having been subjected to a stripping with hydrogen or another inert gas.

Hydrogen is preferred. Gas that is inert relative to the hydrotreated and/or hydrocracked effluent, for example nitrogen, is called inert gas. Water vapor is not part of the inert gases of the invention.

After stripping, the liquid effluent is compressed before being recycled.

Very varied feedstocks can be treated, which have an initial boiling point of 100° C. or more. Generally, they contain at least 20% by volume (for example the gas oils) and often at least 80% by volume (for example the VGO and DAO) of compounds that boil above 340° C. Preferably, the feedstocks have a boiling point T5 that is greater than 340° C. and better yet greater than 370° C., i.e., 95% of the compounds that are present in the feedstock have a boiling point that is greater than 340° C. and better yet greater than 370° C.

The nitrogen content of the hydrocarbon feedstocks that are treated in the process according to the invention is usually greater than 100 ppm and preferably between 500 and 5,000 ppm by weight, in a more preferred manner between 700 and 4,000 ppm by weight, and in an even more preferred manner between 1,000 and 4,000 ppm. Generally, the sulfur content is between 0.01 and 5% by weight, and more generally between 0.2 and 4%.

These feedstocks that are well suited for this process are atmospheric or vacuum distillates that are obtained from the direct distillation of crude or conversion processes, deasphalted oils (DAO), oils that are obtained from units for extraction of aromatic compounds of lubricating oil bases or are obtained from dewaxing of lubricating oil bases by themselves or in a mixture.

A feedstock can be, for example, an LCO (light cycle oil), an atmospheric distillate, and a vacuum distillate, for example diesels that are obtained from the direct distillation of crude or conversion units such as the FCC, the coker, or the viscoreduction unit. This can also be a feedstock that is obtained from units for extraction of aromatic compounds from lubricating oil bases or obtained from dewaxing with solvent of the lubricating oil bases, or else a distillate that is obtained from desulfurization or hydroconversion of RAT (atmosphere residues) and/or RSV (vacuum residues), or else any mixture of the feedstocks cited above. The list of feedstocks above is not limiting.

The catalysts for hydrotreatment and/or hydrocracking are conventional catalysts. The invention sees its effect reinforced when acid catalysts are involved.

The acid catalysts for hydrotreatment and/or hydrocracking are all of the bifunctional type combining an acid function with a hydrogenating function. The acid function is provided by substrates with large surface areas (150 to 800 m²g⁻¹ generally) that exhibit a surface acidity, such as the halogenated aluminas (chlorinated or fluorinated in particular), the combinations of boron and aluminum oxides, the silica-aluminas that may or may not be amorphous, and the zeolites.

The hydrogenating function is provided either by one or more metals of the group VIII of the periodic table, or by a combination of at least one metal of group VIB of the periodic table and at least one metal of group VIII.

The catalyst comprises at least one crystallized acid function such as a Y zeolite, or an amorphous acid function such as a silica-alumina, at least one matrix, and one hydro-dehydrogenating function. Optionally, it can also contain at least one element that is selected from among boron, phosphorus and silicon, at least one element of group VIIA (chlorine, fluorine, for example), at least one element of group VIIB (manganese, for example), and at least one element of group VB (niobium, for example).

These are most often catalysts with a substrate that contains silica-alumina or at least one zeolite. It is possible to cite the catalysts that contain at least one element of group VIII and at least one element of group VIB (for example, NiMo, CoMo, NiCoMo, NiW) that are deposited on an acid substrate, for example a substrate that contains silica-alumina, a zeolitic substrate (for example a substrate that contains the Y zeolite). These catalysts can contain at least one dopant, such as phosphorus.

The operating conditions are conventional. The use of the process according to the invention makes it possible to lower the temperatures and therefore to increase the service life of the catalyst, or it makes it possible to enhance the conversion when the procedure is performed with hydrocracking.

In general, the procedure is performed at a temperature that is greater than 200° C., often between 250 and 480° C., advantageously between 320 and 450° C., preferably between 330 and 425° C., under a pressure that is often between 5 and 25 MPa, preferably less than 20 MPa, whereby the volumetric flow rate is between 0.1 and 20 h⁻¹, preferably between 0.1 and 6 h⁻¹, and preferably between 0.2 and 3 h⁻¹, and the quantity of hydrogen that is introduced is such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 10 and 5,000 l/l, and most often between 50 and 2,000 l/l, and more specifically between 50 and 1,000 l/l.

As regards hydrocracking, the conversions per pass into products that have boiling points of less than 340° C., and better less than 370° C., are greater than 30% by weight and in an even more preferred manner between 40 and 95% by weight.

The hydrotreatment and/or hydrocracking stage can be

-   -   A hydrotreatment stage,     -   A hydrocracking stage, generally a mild hydrocracking (pressures         of less than 110-120 bar),     -   A hydrotreatment stage followed by hydrocracking without         separation between hydrotreatment and hydrocracking (called         “single-stage hydrocracking”),     -   A hydrotreatment stage followed by hydrocracking with separation         (called intermediate separation) between hydrotreatment and         hydrocracking,     -   A hydrotreatment stage followed by a first hydrocracking,         separation of the products, and treatment of the unconverted         fraction in another hydrocracking (called “two-stage         hydrocracking”).

The process can be performed according to 2 methods, as has already been mentioned above.

According to a first method (called conventional method), the gaseous hydrogen is brought into contact with the feedstock and the recycled effluent, and the mixture is sent into the stage for hydrotreatment and/or hydrocracking.

In the second method (called without circulation of gaseous hydrogen through the catalytic bed(s)), the nitrogen feedstock and optionally the recycled portion are brought into contact with the gaseous hydrogen, and then are subjected to a flash separation (separation of undissolved gaseous hydrogen) and are sent to the stage for hydrotreatment and/or hydrocracking. This flash can be separated from the reactor or integrated (located in the same chamber as the reactor), as has been described above.

The process is then performed according to the method called without circulation of gaseous hydrogen through the catalytic bed(s), which corresponds more exactly to less than 10% of hydrogen gas per total volume of the reactor for hydrotreatment and/or hydrocracking.

At the end of the stage for hydrotreatment and/or hydrocracking, the effluent is generally subjected to a separation of the gaseous phase. Various means are used in the processes of the prior art, and most often the procedure is performed with a flash separation, and then optionally a separation with stripping, and finally an atmospheric distillation that can be followed by a vacuum distillation (and that is most often followed by a vacuum distillation).

According to the invention, the portion of the effluent that is recycled has been subjected to a separation by stripping with hydrogen or another gas, regardless of the method (described above) that is used.

Thus, the effluent in its entirety can be subjected to stripping by hydrogen, and a portion is recycled to the hydrotreatment and/or hydrocracking stage; the other portion is sent, for example, to distillation.

In the existing units, this comes down to adding a stripper or to transforming the flash separator into a stripper.

According to another advantageous arrangement on existing units, stripping with hydrogen (or another gas) according to the invention is implemented only on the recycled portion.

Thus, in one embodiment of this arrangement, before separation of the gaseous phase, at least one portion of the effluent that is obtained from the hydrotreatment and/or hydrocracking stage is separated to be recycled to said stage, whereby said part is subjected to a separation by stripping with hydrogen.

Also, in another embodiment, the effluent that is obtained from the hydrotreatment and/or hydrocracking stage is subjected to a flash separation, and a portion of the liquid phase that is obtained from the flash separation is subjected to a separation by stripping with hydrogen before being recycled to said stage.

The implementation of the process according to the invention is then extremely simple since it is sufficient to add a stripper (preferably with hydrogen) to the recycling pipe (whether it is at the outlet of the reactor or the outlet of the flash separator), which avoids providing significant modifications to the existing installation.

The stripping according to the invention is implemented with a minimum pressure drop, i.e., most often at most 5 bar (0.5 MPa); generally, it is between 0.5 and 5 bar. The pressure drop is selected to be compatible with the good operating conditions of the recycling pump in the case of an existing unit.

The stripping temperature is close to that of the reactor; generally, it is on the order of 320-450° C.

The quantity of hydrogen necessary for the stripping is 0.2-1% by weight relative to the fresh feedstock (without recycling), and preferably 0.5-0.7%.

At least 80% and most often at least 90% of the ammonia is eliminated from the effluent before recycling. Also, this stripping makes it possible to reduce significantly the H₂S that is recycled at the top of the reactor.

The ammonia content of the recycled liquid effluent is less than 100 ppm by weight.

The gaseous phase that exits from the stripping is treated so as to recover a more or less pure hydrogen that can be recycled as stripping gas.

In a general way, the hydrogen that enters into the stripper exhibits a purity (expressed in terms of volume) of at least 80%, preferably at least 90%, and also preferably at least 95%, and even at least 99%.

The gaseous phase that exits from the stripping undergoes a treatment that comprises a low-temperature high-pressure separation (called “cold high pressure separator”) with injected water and a cooling of the gaseous phase, whereby the gaseous phase that is obtained from this separation can be subjected to washing with one or more amine(s); it is obtained from hydrogen that in general exhibits a purity (expressed in terms of volume) of at least 90%, and most often of at least 95%.

This hydrogen with a reduced contaminant content—in particular of sulfur molecules—can be recycled (after purging) in part at least with stripping, optionally with the addition of make-up hydrogen (“make-up”) to increase the purity (for example to at least 99%), and after compression.

This hydrogen can also undergo a purification treatment (which is preferably a membrane separation, a separation in a PSA, or a separation by cryogenics), and the hydrogen that is obtained with a purity that is generally at least 99% is, after compression, recycled at least in part to the stripping.

The purified hydrogen that is obtained with a purity (expressed in terms of volume) of at least 99% is then used, after compression, as make-up hydrogen in the process and optionally at the level of stripping.

The combination of these arrangements is also possible.

The invention is illustrated in the attached figures:

FIG. 1 shows a method that is called without circulation of gaseous hydrogen with stripping of the entire effluent,

FIGS. 2 and 3 show a stripping of only the recycled effluent,

FIG. 4 shows a recycling of slightly purified hydrogen,

And FIG. 5 shows a recycling of purified hydrogen.

These figures are commented on with the preferred use of hydrogen with stripping. Furthermore, for the convenience of reading, a flash separator outside of the reactor was shown, which could equally possibly be a flash integrated with the reactor (disengagement zone).

In FIG. 1, the nitrogen feedstock 1 and the recycled effluent 17 are brought into contact in the chamber 3 with the gaseous hydrogen 2, which is generally make-up hydrogen. The mixture 4 is flashed in the flash separator 5, the gaseous hydrogen is evacuated via the pipe 6, and the liquid 7 that is saturated with dissolved H2 is sent into the reactor 8 where the hydrotreatment and/or hydrocracking stage takes place, whereby the reactor contains at least one catalyst bed. A single reactor was shown, but it is quite obvious that several reactors in a series can be used.

The undissolved gas is evacuated via the pipe 9, and the hydrotreated and/or hydrocracked effluent is evacuated via the pipe 10. The pressure drop of the valve 11, stripper and line unit is controlled by the valve 11 to be at most 5 bar. The effluent enters via the pipe 10 a into the stripper 12.

The hydrogen is brought in there by the pipe 13, whereby the gaseous phase is evacuated by the pipe 14 and the liquid effluent by the pipe 15.

A portion of the liquid effluent is recycled by the pipe 16 via a pump 16 a, by a pipe 17 at the chamber 3 (most often mixed with the feedstock as in the figure) and/or by the pipe(s) 18 a and 18 b (dotted lines in the figure) at the inlet of the reactor 8 without passing through the hydrogen saturation.

The other portion 15 a of the liquid effluent continues the stages of the hydrotreatment and/or hydrocracking process, which generally consist of one or more stages for separation by rectification (debutanizer . . . ), and then distillation(s).

FIG. 2 takes on the same type of process (the references are repeated), but with modification after the reactor 8. In this configuration of FIG. 2, the process of the prior art is preserved at the level of separations, i.e., the effluent that exits from the reactor 8 is flashed (flash separator 23), which requires a pressure drop (valve 22) that is greater than 5 bar to be effective, and which is generally at least 7 bar. The gaseous phase is evacuated by the pipe 24 and the liquid effluent by the pipe 25.

A portion of the liquid effluent is sampled to be recycled by the pipe 26, and it enters into the stripper 12.

The hydrogen is brought there via the pipe 13; the gaseous phase is evacuated by the pipe 14, and the liquid effluent by the pipe 15.

The liquid effluent is recycled via a pump 26 a and by a pipe 17 at the chamber 3 (most often mixed with the feedstock as in the figure) and/or by the pipe or pipes 18 a and 18 b (dotted lines in the figure) at the inlet of the reactor 8 without passing through the hydrogen saturation.

The other portion 25 a of the liquid effluent continues the stages of the hydrotreatment and/or hydrocracking process, which generally consist of one or more stages for separation by rectification (debutanizer . . . ) and then distillation(s).

FIG. 3 takes on the same type of process as FIG. 2, but the recycled effluent is a portion of the effluent that is obtained from the reactor 8 with a minimized pressure drop (valve 20) that flows through the pipe 21.

A portion of the effluent that is obtained from the reactor 8 is sampled to be recycled by the pipe 21 and enters into the stripper 12.

The hydrogen is brought there by the pipe 13; the gaseous phase is evacuated by the pipe 14 and the liquid effluent by the pipe 15.

The liquid effluent is recycled via a pump 21 a and by a pipe 17 at the chamber 3 (most often mixed with the feedstock as in the figure) and/or by the pipe(s) 18 a and 18 b (dotted lines in the figure) at the inlet of the reactor 8 without passing through the hydrogen saturation.

The other portion of the effluent that is obtained from the reactor 8 is flashed as described by FIG. 2, and then the portion 25 a of the liquid effluent that exits from the flash separator 23 continues the stages of the hydrotreatment and/or hydrocracking process, which generally consist of one or more stages for separation by rectification (debutanizer . . . ), and then distillation(s).

FIGS. 4 and 5 relate to the treatment of the gaseous phase that is separated with the stripper; embodiments are exhibited there that can be combined.

In these figures, the stripper 12 receives the stripper effluent 10 a, and the stripping hydrogen enters by the pipe 13 a; the separated gaseous phase is evacuated by the pipe 14 and the liquid phase by the pipe 12 a. The subsequent treatments (subsequent separations, for example, shown in the preceding figures) are not recorded in these figures but can quite obviously be integrated in these diagrams.

The gaseous phase of the pipe 14 is first washed with water in the flask 32, whereby the washing water is brought by the pipe 30, and the gaseous phase and optionally the washing water are cooled in advance, for example in an exchanger 31.

The aqueous phase that contains washing water is evacuated from the flask 32 by the pipe 33, the hydrocarbon phase by the pipe 34, and the washed gaseous phase by the pipe 35. The hydrocarbon phase can be recycled in part with the stripper or can be sent into the subsequent separations of the process.

The purification is obviously not perfect and in each phase, contaminants are found, but in small quantities.

This operation, which is well known to one skilled in the art, makes it possible to prevent the formation of ammonia salts that can lead to corrosion and also to clogging of the equipment.

The washed phase of the pipe 35 is subjected to washing with at least one amine in a flask 36, whereby said amine is brought by the pipe 37 (it is recalled that this operation is optional, but preferred in the invention). The amine-washed gaseous phase is evacuated by the pipe 39 and the amine by the pipe 38.

This operation, which is well known to one skilled in the art, makes it possible to reduce the content of contaminants such as H₂S to less than 100 ppm by volume.

This portion described above is common to the embodiments. The difference between the embodiments of FIGS. 4 and 5 is in the recycling of the hydrogen with the stripper.

The gaseous phase that is optionally washed with amine generally contains at least 90% and most often at least 95% hydrogen. The purity is adequate for using this phase as a stripping hydrogen. This is what is illustrated in FIG. 4 where a portion of said gaseous phase is sent by the pipe 41 to a compressor 43 to be recycled at the pressure of the stripper via the pipe 13 a. It is generally preferable to bring (pipe 42 a) make-up hydrogen, which generally exhibits a purity of more than 99%, which passes (FIG. 4) or does not pass (not shown) into the compressor 43.

The other portion (pipe 13 b) can be used in this process or in another process that is performed on site.

According to its purity and its pressure level, the make-up hydrogen can equally possibly be introduced, for example, after the compressor 43 (for example line 42 b), in the separated gaseous phase with the stripper (for example, line 42 c).

In FIG. 5, the amine-washed gaseous phase undergoes a subsequent purification in a known purification means 45 (membrane, PSA, cryogenic apparatus, . . . ) for bringing the hydrogen to the purity of make-up hydrogen.

The gaseous portion that contains the contaminants is evacuated by the pipe 46 and the purified hydrogen by the pipe 42.

This hydrogen is in part recycled (pipe 13 a) to the stripper 12 after compression (compressor 43); the other portion (pipe 13 b) is used as make-up hydrogen preferably in this hydrotreatment/hydrocracking process (at the level of the reactor or the mixing chamber according to the operating mode of the process) or more generally in the refinery.

The hydrogen that is introduced to stripping has been compressed and reheated. Preferably, it was reheated by the gaseous phase that exits from the stripping, for example in the exchanger 31.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. Process for hydrotreatment and/or hydrocracking of nitrogen feedstocks in which a portion of the hydrotreated and/or hydrocracked effluent is recycled to the hydrotreatment and/or hydrocracking stage after having been subjected to stripping with hydrogen or another inert gas.
 2. Process according to claim 1, in which the hydrogen that enters into the stripper exhibits a purity (expressed in terms of volume) of at least 80%, preferably at least 90%, and also preferably at least 95%, and even at least 99%.
 3. Process according to claim 1 in which the nitrogen feedstock and optionally the recycled portion is brought into contact with the gaseous hydrogen, and then it is subjected to a flash separation and is sent to the hydrotreatment and/or hydrocracking stage.
 4. Process according to claim 1, in which the nitrogen feedstock has a nitrogen content that is greater than 100 ppm and preferably between 500 and 5,000 ppm by weight, in a more preferred manner between 700 and 4,000 ppm by weight, and in an even more preferred manner between 1,000 and 4,000 ppm; the sulfur content is between 0.01 and 5% by weight, and more generally between 0.2 and 4%.
 5. Process according to claim 1, in which the feedstock is selected from the group that is formed by the atmospheric or vacuum distillates that are obtained from the direct distillation of crude or conversion processes, the deasphalted oils (DAO), the oils that come from units for extraction of aromatic compounds from lubricating oil bases or that are obtained from dewaxing of lubricating oil bases, by themselves or in a mixture.
 6. Process according to claim 1, in which the hydrogen stripping is implemented only on the recycled portion.
 7. Process according to claim 1, in which before separation of the gaseous phase, at least one portion of the effluent that is obtained from the hydrotreatment and/or hydrocracking stage is separated to be recycled to said stage, whereby said portion is subjected to a hydrogen stripping separation.
 8. Process according to claim 1, in which the effluent that is obtained from the hydrotreatment and/or hydrocracking stage is subjected to a flash separation, and a portion of the liquid phase that is obtained from the flash separation is subjected to a hydrogen stripping separation before being recycled to said stage.
 9. Process according to claim 1, in which the effluent in its entirety is subjected to hydrogen stripping; a portion is recycled to the hydrotreatment and/or hydrocracking stage.
 10. Process according to claim 1, in which the stripping is implemented with a pressure drop of at most 5 bar (0.5 MPa), generally between 0.5 and 5 bar, and the stripping temperature is 320-450° C.; the quantity of hydrogen is 0.2-1% by weight relative to the fresh feedstock (without the recycling), and preferably 0.5-0.7%.
 11. Process according to claim 1, in which the gaseous phase that exits from the stripping undergoes a treatment that comprises a low-temperature high-pressure separation with injected water and a cooling of the gaseous phase; the hydrogen having a purity of at least 90%, and most often at least 95%, is at least partially recycled, and after compression, optionally with supply of make-up hydrogen, to the stripping.
 12. Process according to claim 1, in which the gaseous phase that is obtained from this separation is subjected to washing with at least one amine; the hydrogen having a purity of at least 90%, and most often at least 95%, is at least partially recycled and after compression, optionally with supply of make-up hydrogen, to the stripping.
 13. Process according to claim 1, in which the gaseous phase that exits from the stripping undergoes a treatment that comprises a low-temperature, high-pressure separation with the injected water and a cooling of the gaseous phase, whereby the gaseous phase that is obtained from this separation is optionally subjected to washing with at least one amine; the hydrogen having a purity of at least 90%, and most often at least 95%, undergoes a purification treatment, preferably selected from the group that is formed by membrane separation, separation in a PSA, or a separation by cryogenics; hydrogen that is obtained with a purity of at least 99% is at least partially recycled after compression to the stripping.
 14. Process according to claim 1, in which the catalyst contains at least one element of group VIII and at least one element of group VIB that are deposited on an acid substrate, whereby the catalyst optionally contains phosphorus, and the hydrotreatment and/or hydrocracking stage is implemented at a temperature of more than 200° C., often between 250 and 480° C., advantageously between 320 and 450° C., preferably between 330 and 425° C., under a pressure of between 5 and 25 MPa, preferably less than 20 MPa, whereby the volumetric flow rate is between 0.1 and 20 h⁻¹, and preferably between 0.1 and 6 h⁻¹, preferably between 0.2 and 3 h⁻¹, and the quantity of hydrogen that is introduced is such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 10 and 5,000 l/l and most often between 50 and 2,000 l/l.
 15. Process according to claim 1, in which the hydrogen that is introduced to stripping has been compressed and reheated. 